System for monitoring the location of transgenes

ABSTRACT

A novel strategy for monitoring the location of a transgene in a mammal is disclosed. A sodium iodide symporter is genetically fused to either the N-terminus or C-terminus of the product of a transgene through a linker peptide which bears the recognition sequence of a host cell protease. Expression of the transgene confers the activity of the sodium iodide symporter (NIS) to a host cell which expresses the transgene. Subsequent administration of labeled iodine results in transport of the labeled iodine into the cell bearing the NIS, which can then be localized and measured using standard imaging techniques. The system is particularly useful for monitoring the location of therapeutic transgenes and tissue-specific distribution of the therapeutic gene product.

CROSS-REFERENCE TO RELATED APPLICATION

This application as a divisional of U.S. application Ser. No. 10/428,868, filed May 1, 2003, which is a continuation of U.S. application Ser. No. 09/640,198 (now U.S. Pat No. 6,586,411, ) filed Aug. 16, 2000. The disclosures of the prior applications are considered part of (and are incorporated by reference in) the disclosure of this application.

BACKGROUND OF THE INVENTION

In the context of gene therapy in a mammal, it is important to monitor the localization of a transgene. Where the transgene encodes a therapeutic polypeptide, such as a protein targeted to kill cancer cells, it is advantageous to have information as to the location, that is, the specific organs, tissues and/or cells which are expressing the polypeptide. There is a need in the art for methods and materials that permit the monitoring of tissue- or cell-specific transgene expression without the requirement to sample and directly test genetically modified cells or tissues.

SUMMARY OF THE INVENTION

The invention contemplates a method of monitoring the location of a transgene in a mammal, comprising the steps of (a) administering to a mammal in need thereof nucleic acid comprising a transgene and a sequence encoding a sodium-iodide symporter (NIS), wherein expression of NIS in cells permits cellular uptake of iodine (b) administering to a mammal labeled iodine in an amount sufficient to permit transport of the labeled iodine by MS and detection of transported labeled iodine; and (c) detecting the location of the transported labeled iodine in the mammal as an indication of the location of the transgene.

In some embodiments, the step of detecting is performed quantitatively to determine the amount of transported labeled iodine in a mammal. The location of the transported labeled iodine is indicative of the location of NIS, whereby the location of NIS is indicative of the location of the transgene.

The invention also provides a method of monitoring the location of a transgene in a mammal, comprising the steps of (a) transfecting a host cell ex vivo with nucleic acid comprising a transgene and a sequence encoding and expressing NIS, wherein the MS permits cellular uptake of iodine by the host cells; (b) introducing the transfected host cell into a mammal; (c) administering to the mammal labeled iodine in an amount sufficient to permit transport of the labeled iodine by MS and detection of transported labeled iodine; and (d) determining the location of transported labeled iodine in the mammal; whereby the location of transported labeled iodine is indicative of the location of the transgene.

In preferred embodiments, the labeled iodine is radioactive iodine.

The invention also provides a nucleic acid construct comprising a chimeric gene comprising the transgene and the sequence encoding an NIS, wherein the chimeric gene also comprises a sequence encoding a protease-cleavable linker between the transgene and the sequence encoding NIS.

In a further embodiment, the sequence encoding the protease-cleavable amino acid linker comprises a sequence encoding an auto-cleaving sequence.

The invention also provides a nucleic acid construct comprising a first promoter operably associated with the transgene and a second promoter operably associated with the sequence encoding MS.

The invention further provides a nucleic acid construct comprising a chimeric gene comprising a transgene and the sequence encoding NIS, wherein the chimeric gene also comprises between the transgene and the sequence encoding MS, a sequence encoding an internal ribosome entry site.

In a preferred embodiment, the sequence encoding a protease cleavable linker is attached to the 5′ end of the transgene.

In another preferred embodiment, the sequence encoding the protease-cleavable linker is attached to the 3′ end of the transgene.

In a preferred series of embodiments, the protease cleavable linker is cleaved by furin, or is identical to a linker present in a cytoplasmic protein.

In another series of preferred embodiments, the transgene encodes a fusogenic polypeptide, the fusogenic polypeptide encodes a viral fusion protein, the fusogenic polypeptide encodes a measles virus H glycoprotein, or the fusogenic polypeptide encodes a gibbon ape leukemia virus envelope glycoprotein.

The invention additionally provides a host cell comprising (a) a nucleic acid construct comprising a sequence encoding a transgene and a sequence encoding a sodium-iodide symporter (NIS), wherein the chimeric gene also comprises a sequence encoding a protease-cleavable linker between the transgene and the sequence encoding NIS; (b) a construct comprising a first promoter operable associated with the transgene and a second promoter is operable associated with the sequence encoding NIS; or (c) a construct comprising a chimeric gene comprising the transgene and the sequence encoding NIS, wherein the chimeric gene also comprises between the transgene and the sequence encoding NIS, a sequence encoding an internal ribosome entry site.

The invention further provides a kit comprising, in a ready to use format, one or more of the nucleic acid constructs described above, and one or more reagents for monitoring the location of the transported labeled iodine.

The invention still further provides a kit comprising, in a ready to use format, a host cell transfected with one or more of the nucleic acid constructs described above, and one or more reagents for monitoring the location of the transported labeled iodine.

In a preferred embodiment, the reagents of the kit include labeled iodine.

In a preferred embodiment, the reagents of the kit include radioactive iodine.

The invention thus provides the art with methods and materials for conveniently and effectively monitoring the tissue-specific distribution of expressed transgenes in cells, tissues, animals or human patients without the need for disruptive sampling methods including surgery.

As used herein, “cell-associated protease” refers to any protease within the cell, such as a protease located in the cytoplasm, or within, or associated with an organelle. As used herein, “cell-associated protease” also refers to any protease associated with the cell, including, but not limited to a protease located on the cell surface or in the extracellular space near the cell surface, such that the protease cleaves a peptide with the appropriate sequence near the cell surface.

As used herein, “mammal” refers to any warm blooded organism of the class Mammalia, including, but not limited to rodents, feline, canine, or ungulates. In preferred embodiments of the invention, a “mammal” is a human.

As used herein, “transgene” refers to any nucleic acid sequence introduced into a cell and which encodes a polypeptide of interest. As used herein a “transgene” can be a gene which is endogenous to the mammal of the present invention, and which may or may not be endogenously expressed by the cells of the invention into which it is introduced. According to the present invention, a “transgene” can be applied to remedy a disease condition in the process known as gene therapy.

As used herein, “auto-cleaving sequence” refers to a short polypeptide sequence of between 10 and 20 amino acids, but preferably between 12 and 18 amino acids, but more preferably between 15 and 17 amino acids, in which cleavage of the propeptide at the C-terminus occurs cotranslationally in the absence of a cell associated protease. Moreover, cleavage can occur in the presence of heterologous sequence information at the 5′ and/or 3′ ends of the “auto-cleaving sequence”. An example of an “auto-cleaving sequence” useful in the present invention is the that of the foot and mouth disease virus (FMDV) 2A propeptide, in which cleavage occurs at the C-terminus of the peptide at the final glycine-proline amino acid pair. Cleavage of FMDV 2A propeptide is independent of the presence of other FMDV sequences and can generate cleavage in the presence of heterologous sequences. Insertion of this sequence between two protein coding regions results in the formation of a self-cleaving chimera which cleaves itself into a C-terminal fragment which carries the C-terminal proline of the 2A protease on its N-terminal end, and an N-terminal fragment that carries the rest of the 2A protease peptide on its C-terminus (P. deFelipe et al., Gene Therapy 6: 198-208 (1999)). Thus, instead of using a cleavage signal recognizable by a cell-associated protease, the self-cleaving FMDV 2A protease sequence can be employed to link the NIS to the polypeptide encoded by the transgene, resulting in spontaneous release of the NIS from the polypeptide encoded by the transgene.

As used herein, a “fusogenic polypeptide” refers to a membrane glycoprotein, including, but not limited to Type I and Type II membrane glycoproteins, which kill cells on which they are expressed by fusing the cells into a partial or complete multinucleated syncytia, which die by sequestration of cell nuclei and subsequent nuclear fusion. Examples of “fusogenic polypeptides” include, but are not limited to gibbon ape leukemia virus and measles virus H glycoprotein.

As used herein, “detecting” refers to the use any in vivo, ex vivo, or in vitro imaging technique capable of measuring a radio-labeled moiety, including, but not limited to standard single positron emission computed tomography (SPECT) or positron emission tomography (PET) imaging systems, used to measure the amount of labeled iodine in a mammal. Labeled iodine of the present invention is “detected” if the levels of labeled iodine measured following administration of one or more of the nucleic acid constructs described above, or the host cells transfected with one or more of the nucleic acid constructs described above are at all higher than the levels measured prior to administration. Labeled iodine of the present invention is also “detected” if it is localized to one or more organs, tissues, or cells following the administration of one or more of the nucleic acid constructs described above, or the host cells transfected with one or more of the nucleic acid constructs described above, that it was not localized to prior to the administration of the constructs or cells. According to the invention, labeled iodine is “detected” if the quantitative or semi-quantitative measurements of labeled iodine yield levels which are between 0.001-90% of the administered labeled iodine dose, preferably between 0.01-70%, preferably between 0.1-50%, more preferably between 1.0-20%, more preferably between 5-10% of the administered labeled iodine dose. In a preferred embodiment, the concentration of labeled iodine in organs, tissues, or cells can be determined by comparing the quantity of labeled iodine measured by methods of the invention, including, but not limited to SPECT or PET, to a standard sample of known labeled iodine concentration.

As used herein, “transported” refers to the movement of labeled iodine from the outside of one or more cells to the inside of one or more cells as a result of the expression of an NIS by the cell or cells which “transported” the labeled iodine. Labeled iodine is considered to be “transported” if the measured levels of iodine in organs, tissues or cells of the invention are between 0.001-90% of the administered labeled iodine dose, preferably between 0.01-70%, preferably between 0.1-50%, more preferably between 1.0-20%, more preferably between 5-10% of the administered labeled iodine dose.

As used herein, the biological activity of an NIS polypeptide, referred to herein as “NIS activity” or “NIS function” is the transport or sequestration of iodine across the cell membrane, i.e., from outside a cell to inside a cell. NIS is an intrinsic membrane glycoprotein with 13 putative transmembrane domains which is responsible for the ability of cells of the thyroid gland to transport and sequester iodide. AN NIS polypeptide useful in the invention with “NIS activity” or “NIS function” thus is a membrane glycoprotein with a transmembrane domain and is capable of transporting iodine if the polypeptide is present in a thyroid cell, and can also transport iodine in a non-thyroid cell type described herein.

As used herein, “a sequence encoding an NIS”, or an “NIS gene” refers to a nucleotide sequence encoding a polypeptide having the activity of a sodium iodide symporter (NIS). Examples of NIS nucleotide sequences and amino acid sequences include, but are not limited to, SEQ ID Nos 1 and 3 and SEQ ID Nos 2 and 4 respectively, as shown in FIGS. 1-4. NIS nucleotide and/or amino acid sequences also include, but are not limited to homologs or analogs of the nucleotide and/or amino acid sequences of FIGS. 1-4, wherein “homologs” are natural variants of NIS which retain NIS activity, and “analogs” are engineered variants of NIS which retain NIS activity.

An advantage of the present invention is that the transgene location can be monitored with out adversely affecting the mammal or the cell. That is, NIS is a self-protein, and as such does not stimulate a host immune reaction. Furthermore, the NIS functions solely to sequester iodine into a cell, which does not adversely affect normal cellular function, or overall cell biology.

Further features and advantages of the invention will become more fully apparent in the following description of the embodiments and drawings thereof, and from the claims

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 displays the nucleotide sequence of SEQ ID NO: 1 which encodes human NIS.

FIG. 2 displays the amino acid sequence of human NIS (SEQ ID NO: 2).

FIG. 3 displays the nucleotide sequence of SEQ ID NO: 3 which encodes rat NIS.

FIG. 4 displays the amino acid sequence of rat NIS (SEQ ID NO: 4)

FIG. 5 displays a schematic representation of the sodium-iodide symporter in the cell membrane.

FIG. 6 displays the expression constructs of the present invention in which the sequence encoding the NIS is linked to the N-terminus of the gibbon ape leukemia virus (GALV) envelope protein via a furin cleavable linker. The expressed polypeptide includes, from N-terminal to C-terminal, NIS (represented by the last four amino acids (ETNL) of SEQ ID NOs:2 and 4), a furin cleavable linker (RLKRGSR; SEQ ID NO:27), a Not 1 site, a factor Xa cleavage site (FXA; represented by the amino acids IEGR (SEQ ID NO:28)), and GALV envelope protein (represented by the amino acids SLQNK (SEQ ID NO:29)).

FIG. 7 displays an expression construct of the present invention in which the sequence encoding the NIS is linked to the C-terminus of measles virus H glycoprotein via a furin cleavable linker or via a non-cleavable linker. The expressed polypeptide includes, from N-terminal to C-terminal, measles virus H glycoprotein (represented by the amino acids REDGTN (SEQ ID NO:30)), an Sfi 1 site (represented by the amino acids AAQPAAA (SEQ ID NO:31) or AAQPA (SEQ ID NO:32)), a cleavable or non-cleavable linker (represented by RLKR (SEQ ID NO:33) and GGGGS (SEQ ID NO:34), respectively), NIS (represented by the last four amino acids (ETNL) of SEQ ID NOs:2 and 4), and a Not 1 site.

FIG. 8 displays a schematic representation of a host cell of the invention which contains a nucleic acid construct comprising a first promoter operably linked to a sequence encoding NIS at the 5′ end of the construct and a second promoter operably linked to a transgene at the 3′ end of the construct.

FIG. 9 displays a schematic representation of a host cell of the invention which contains a nucleic acid construct comprising a first promoter operably linked to a sequence encoding NIS at the 3′ end of the construct and a second promoter operably linked to a transgene at the 5′ end of the construct.

FIG. 10 displays a mixed host cell population comprising one or more cells which contain a nucleic acid construct comprising a first promoter operably linked to a transgene and a second promoter operably linked to a sequence encoding NIS (marker cells), and one or more cells which contain a nucleic acid construct comprising a transgene alone.

FIG. 11 displays a mixed host cell population comprising one or more cells which contain a nucleic acid construct comprising a sequence encoding NIS (marker cells), and one or more cells which contain a nucleic acid construct comprising a transgene.

DETAILED DESCRIPTION

The present invention provides a novel method of monitoring the distribution in a cell or tissue of a transgene in vivo. The present invention encompasses localizing the presence and/or expression of a transgene comprising administering to a mammal a nucleic acid comprising (a) a chimeric nucleic acid sequence encoding the transgene and a sequence encoding the NIS, wherein the chimeric construct also comprises a sequence encoding a protease-cleavable linker between the transgene and the sequence encoding the NIS, (b) a nucleic acid sequence wherein a first promoter is operably associated with the transgene and a second promoter is operably associated with the sequence encoding the NIS, or (c) a chimeric gene comprising the transgene and the sequence encoding the NIS, wherein the chimeric gene also comprises, between the transgene and the sequence encoding the NIS, a sequence encoding an internal ribosome entry site; or administering to a mammal a cell transfected with a nucleic acid construct of one or more of (a), (b), or (c) as described above.

According to an embodiment of the invention a NIS is genetically fused to the N-terminus or the C-terminus of the polypeptide product of a transgene such that the activities of both polypeptides are present in the polypeptide. According to a preferred embodiment of the invention, the NIS and the polypeptide product of the transgene are associated through a linker polypeptide that is cleavable by a cell-associated protease.

The protease cleavage signal is chosen such that at some point during the subsequent folding, assembly, and transport of the molecule within a cell, a cell-associated protease cleaves the NIS from the transgene product. The mammal is subsequently administered labeled iodine, which is transported into any cell which possesses an NIS. The labeled iodine can then be localized using non-invasive imaging techniques such as SPECT or PET, such that localization of labeled iodine indicates the expression of the transgene product.

In a variation of this embodiment, the construct does not encode a protease-cleavable linker, but instead the NIS is operationally associated with a different promoter from that which is associated with the transgene. In yet another variation of this embodiment, the construct does not encode a protease-cleavable linker, but instead the construct is transcribed to a polycistronic mRNA which comprises a ribosome entry site between the transgene and the sequence encoding the NIS.

Still another embodiment of the invention provides another method for monitoring the localization of a transgene. A cell that has been transfected ex vivo with the nucleic acid construct described above (host cell) is introduced into a mammal. Expression of the transgene and NIS from the host cell will lead to the transport of labeled iodine from the outside to the inside of the host cell. The labeled iodine may be localized by standard SPECT or PET scan as an indication of the location of transgene expression. In a variation of this embodiment, the cell is transfected with a construct that does not encode a protease-cleavable linker. Instead, the NIS is operationally associated with a different promoter from that which is associated with the transgene. In another variation of this embodiment, the cell is transfected with a construct that is transcribed to a polycistronic mRNA which comprises an internal ribosome entry site between the transgene and the sequence encoding the NIS. Because of the position of the ribosome entry site, both the transgene product and the NIS are expressed separately without the need for protease cleavage.

Yet another embodiment of the invention provides a method of monitoring the location of a therapeutic transgene. In this embodiment, the nucleic acid construct of this invention is used to transfect a cell as explained in either of the two previous embodiments. In this case, the transgene is a therapeutic gene which is introduced into a mammal to remedy a functional deficiency, treat a pathological condition, or destroy certain cells of the mammal by the activity of the transgene product. Detection of transgene localization may be used to gage the progress of therapy, and to insure that the tissue-specific distribution of the transgene is appropriate for the intended treatment. In some versions of this embodiment, a transgene product which destroys cancer cells is monitored as a means of assessing the effectiveness of the therapy and deciding whether to repeat or adjust the therapy.

The transgene of the present invention is any nucleic acid sequence introduced into a cell. Transgenes can be applied to remedy a disease condition in the process known as gene therapy. The term gene therapy can be applied to any therapeutic procedure in which genes or genetically modified cells are administered for therapeutic benefit. For some uses of the invention the transgene will be one which encodes a polypeptide that selectively kills a certain group of undesired cells such as cancer cells. For example, the transgene can encode a fusogenic polypeptide such as a viral fusion protein or an artificial polypeptide which causes the fusion of cells expressing the polypeptide, resulting in syncytium formation and cell death. The transgene can be introduced into a target cell or host cell by any mechanism of transfer known in the art, including any type of gene therapy, gene transfer, transfection, and the like.

Sodium-Iodide Symporter

Current treatments for thyroid cancers utilize radioactive iodine therapy, given the intrinsic ability of thyroid cells, cancerous or not, to concentrate iodine from extracellular fluid. The iodine trapping activity of thyroidal cells is utilized in diagnosis as well as therapy of thyroid cancer. Functioning thyroid cancer metastases can be detected by administering radioiodine and then imaging with a gamma camera.

Recently, the mechanism mediating iodide uptake across the basloateral membrane of thyroid follicular cells has been elucidated by cloning and characterization of the sodium iodide symporter (FIG. 5; Smanik et al., Biochem Biophys Res Commun. 226:339-45 (1996); Dai et al., Nature. 379:458-60 (1996)). NIS is an intrinsic membrane glycoprotein with 13 putative transmembrane domains which is responsible for the ability of cells of the thyroid gland to transport and sequester iodide. An NIS of the present invention is comprised of a polypeptide having the activity of a sodium iodide symporter, including, but not limited to the polypeptide encoded by the amino acid sequences of SEQ ID Nos 2 and 4 for human and rat respectively, wherein the amino acid sequences of SEQ ID Nos 2 and 4 are encoded by polynucleotide sequences comprising SEQ ID Nos 1 and 3 for human and rat respectively, or an analog thereof. NIS expression in thyroid tissues is dependent upon stimulation of the cells by pituitary-derived thyroid stimulating hormone (TSH) and can therefore be readily suppresses in this tissue by treatment with Thyroxine. TSH-regulated NIS expression is specific for thyroid cells, whereas many other organs do not concentrate iodine due to lack of NIS expression. Cloning and characterization of the human and rat NIS genes (SEQ ID NO: 1 and 3 respectively; GenBank Accession numbers A005796 and U60282 respectively) permits NIS gene delivery into non-thyroid cells, thereby allowing these cells to trap and sequester radio-labeled iodine.

According to the present invention, the NIS functions well as a localization tag for several reasons. The NIS, according to the present invention, is synthesized in the mammal, using the mammals own protein synthetic machinery, and thus is recognized as self, thereby avoiding a potential immune response. Furthermore, the NIS is a useful localization tag according to the present invention as it should have no significant effect on the biological properties of the genetically modified cells. Given that the only known function of the NIS is to transport iodine across the cell membrane, it should not adversely affect endogenous cellular function.

Nucleic Acid Constructs

Central to the use of the invention is the creation and/or use of a nucleic acid construct comprising sequences encoding a transgene, a NIS, and optionally a protease-cleavable linker (FIGS. 6 and 7). The nucleic acid construct can be an expression vector, a plasmid that can be prepared and grown in bacteria, or an engineered virus capable of transfecting the host cell. The nucleic acid sequences of the construct can contain DNA, RNA, a synthetic nucleic acid, or any combination thereof, as known in the art. The nucleic acid construct can be packaged in any manner known in the art consistent with its delivery to a target cell. For example, the construct can be packaged into a liposome, a DNA- or retro-virus, or another structure. The sequences should be arranged so that the protease-cleavable linker peptide, if one is included, is situated between the transgene product and the NIS, resulting in the cleavage of the NIS from the transgene product by a selected protease, which can be a protease that is encountered in the host cell or organism during post-translational processing. One means of accomplishing this is to design the nucleic acid construct such that the sequences encoding both the NIS and the linker polypeptide are attached to either the 3′ end or the 5′ end of the transgene. The sequences encoding each of the three components may be interspersed with other sequences as needed. However, in order for the NIS to be cleaved from the transgene product during processing, it is necessary that the protease cleavable linker sequence be interposed between the transgene product and the NIS.

Promoters of the invention include, but are not limited to any promoter that is operable in a selected host cell according to the invention. Additionally, a promoter of the invention can be the endogenous promoter for NIS or the endogenous promoter for a transgene, or can be any promoter that will be operative in the expression of the sequence encoding the NIS, or the transgene in a host cell of the invention.

Preferably, the sequences encoding each of the three components (the transgene product, the linker, and the NIS) are all under control of a single promoter sequence, resulting in the expression of a fusion protein containing each of the three elements. This assures that the NIS and the transgene product will be synthesized in stoichiometric proportion, which is preferred because it results in similar levels and location of expression for both the transgene product and the NIS. The chosen promoter can be one which regulates the expression of the transgene in a manner consistent with its use in the host organism, for example, in a manner consistent with the intended gene therapy. The expression of the NIS can be driven from a second promoter inserted into the construct or it can be encoded on the same transcript as the transgene, but translated from an internal ribosome entry site. The use of two or more separate promoters is less likely to produce the desired stoichiometry of expression. However, the use of two promoters can, in some embodiments, obviate the need for including a protease-cleavable linker peptide. If the NIS is regulated by a separate promoter, it will be translated separately from the transgene product without requiring proteolysis. While the two promoters regulating the transgene and the NIS can be different, they can also be the same promoter, in which case the expression of both transgene and NIS are quite likely to be parallel, thereby increasing the effectiveness of the NIS for monitoring the tissue-specific distribution of the transgene.

Another alternative strategy to using a protease-cleavable linker is to include an internal ribosome entry site in the construct between the transgene and the coding sequence for the NIS. Internal ribosomal entry sites (IRES, also called ribosomal landing pads) are sequences that enable a ribosome to attach to mRNA downstream from the 5′ cap region and scan for a downstream AUG start codon, for example in polycistronic mRNA. See generally, Miles et al., U.S. Pat. No. 5,738,985 and N. Sonenberg and K. Meerovitch, Enzyme 44: 278-91 (1990). Addition of an IRES between the coding sequences for the transgene product and the NIS permits the independent translation of either the transgene product or the NIS from a dicistronic or polycistronic transcript. IRES sequences can be obtained from a number of RNA viruses (e.g., picornaviruses, hepatitis A, B, and C viruses, and influenza viruses) and DNA viruses (e.g., adenovirus). IRES have also been reported in mRNAs from eukaryotic cells (Macejak and Sarnow, Nature 353: 90-94 (1991) and Jackson, Nature 353: 14015 (1991)). Viral IRES sequences are detailed in the following publications:

Coxsackievirus

-   Jenkins, O., J. Gen. Virol. 68: 1835-1848 (1987) -   Iizuka, N. et al., Virology 156: 64-73 (1987) -   Hughes et al., J. Gen. Virol. 70: 2943-2952 (1989)     Hepatitis A Virus -   Cohen, J. I. et al., Proc. Natl. Acad. Sci. USA 84: 2497-2501 (1987) -   Paul et al., Virus Res. 8: 153-171 (1987)     Poliovirus -   Racaniello and Baltimore, Proc. Natl. Acad. Sci. USA 78: 4887-4891     (1981) -   Stanway, G. et al., Proc. Natl. Acad. Sci. USA 81: 1539-1543 (1984)     Rhinovirus -   Deuchler et al., Proc. Natl. Acad. Sci. USA 84: 2605-2609 (1984) -   Leckie, G., Ph.D. thesis, University of Reading, UK -   Skern, T. et al., Nucleic Acids Res. 13: 2111 (1985)     Bovine Enterovirus -   Earle et al., J. Gen. Virol. 69: 253-263 (1988)     Enterovirus Type 70 -   Ryan, M. D. et al., J. Gen. Virol. 71: 2291-99 (1989)     Theiler's Murine Encephalomyelitis Virus -   Ohara et al., Virology 164: 245 (1988) -   Peaver et al., Virology 161: 1507 (1988)     Encephalomyocarditis Virus -   Palmenberg et al., Nucl. Acids Res. 12, 2969-2985 (1984) -   Bae et al., Virology 170, 282-287 (1989)     Hepatitis C. Virus -   Inchauspe et al., Proc. Natl. Acad. Sci. USA 88: 10293 (1991) -   Okamoto et al., Virology 188: 331-341 (1992) -   Kato et al., Proc. Natl. Acad. Sci. USA 87: 9524-9528 (1990)     Influenza Virus -   Fiers, W. et al., Supramol. Struct. Cell Biochem. (Suppl 5), 357     (1981)     Release of the NIS

For an embodiment of the invention which utilizes a protease cleavable linker between the transgene in the sequence encoding the NIS, the invention permits a great deal of flexibility and discretion in terms of the choice of the protease cleavable linker peptide. The protease specificity of the linker is determined by the amino acid sequence of the linker. Specific amino acid sequences can be selected in order to determine which protease will cleave the linker; this is an important indication of the location of cleavage within the cell or following secretion from the cell and can have a major effect on the release of the NIS. The furin cleavage signal is ideal for cell-associated transgenes that are transported to the cell surface through the Golgi compartment. Cell surface receptors, such as the LDL receptor used for the treatment of hypercholesterolemia or chimeric T cell receptors used for retargeting T cells can therefore be marked using furin-cleavable peptides. For cytoplasmic proteins, it is necessary to use cleavage signals that are recognized by cytoplasmic proteases and to use peptides with appropriate hydrophilic/hydrophobic balance so that they can escape across the plasma membrane.

Proteases useful according to the invention are described in the following references: V. Y. H. Hook, Proteolytic and cellular mechanisms in prohormone and proprotein processing, R G Landes Company, Austin, Tex., USA (1998); N. M. Hooper et al., Biochem. J. 321: 265-279 (1997); Z. Werb, Cell 91: 439-442 (1997); T. G. Wolfsberg et al., J. Cell Biol. 131: 275-278 (1995); K. Murakami and J. D. Etlinger, Biochem. Biophys. Res. Comm. 146: 1249-1259 (1987); T. Berg et al., Biochem. J. 307: 313-326 (1995); M. J. Smyth and J. A. Trapani, Immunology Today 16: 202-206 (1995); R. V. Talanian et al., J. Biol. Chem. 272: 9677-9682 (1997); and N. A. Thornberry et al., J. Biol. Chem. 272: 17907-17911 (1997). In addition, a variety of different intracellular proteases useful according to the invention and their recognition sequences are summarized in Table 1. While not intending to limit the scope of the invention, the following list describes several of the known proteases which might be targeted by the linker and their location in the cell.

Secretory Pathway (ER/Golgi/Secretory Granules)

-   Signal peptidase -   Proprotein convertases of the subtilisin/kexin family (furin, PC1,     PC2, PC4, PACE4, PC5, PC) -   Proprotein convertases cleaving at hydrophobic residues (e.g., Leu,     Phe, Val, or Met) -   Proprotein convertases cleaving at small amino acid residues such as     Ala or Thr -   Proopiomelanocortin converting enzyme (PCE) -   Chromaffin granule aspartic protease (CGAP) -   Prohormone thiol protease -   Carboxypeptidases (e.g., carboxypeptidase E/H, carboxypeptidase D     and carboxypeptidase Z) -   Aminopeptidases (e.g., arginine aminopeptidase, lysine     aminopeptidase, aminopeptidase B)     Cytoplasm -   Prolyl endopeptidase -   Aminopeptidase N -   Insulin degrading enzyme -   Calpain -   High molecular weight protease -   Caspases 1, 2, 3, 4, 5, 6, 7, 8, and 9     Cell Surface/Pericellular Space -   Aminopeptidase N -   Puromycin sensitive aminopeptidase -   Angiotensin converting enzyme -   Pyroglutamyl peptidase II -   Dipeptidyl peptidase IV -   N-arginine dibasic convertase -   Endopeptidase 24.15 -   Endopeptidase 24.16 -   Amyloid precursor protein secretases alpha, beta and gamma -   Angiotensin converting enzyme secretase -   TGF alpha secretase -   TNF alpha secretase -   FAS ligand secretase -   TNF receptor-I and -II secretases -   CD30 secretase -   KL1 and KL2 secretases -   IL6 receptor secretase -   CD43, CD44 secretase -   CD16-I and CD16-II secretases -   L-selectin secretase -   Folate receptor secretase -   MMP 1, 2, 3, 7, 8, 9, 10, 11, 12, 13, 14, and 15 -   Urokinase plasminogen activator -   Tissue plasminogen activator -   Plasmin -   Thrombin -   BMP-1 (procollagen C-peptidase) -   ADAM 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11 -   Granzymes A, B, C, D, E, F, G, and H

An alternative to relying on cell-associated proteases is to use a sequence encoding a self- or auto-cleaving linker. An example of such a sequence is that of the foot and mouth disease virus (FMDV) 2A protease. This is a short polypeptide of 17 amino acids that cleaves the polyprotein of FMDV at the 2A/2B junction. The sequence of the FMDV 2A propeptide is NFDLLKLAGDVESNPGP (SEQ ID NO: 5), which can be encoded by a nucleic acid sequence comprising ttgaagctgaataattttaatcgtcctctgcatctttcgttgggtcctggt (SEQ ID NO: 6). The cleavage occurs at the C-terminus of the peptide at the final glycine-proline amino acid pair. Cleavage of FMDV 2A propeptide is independent of the presence of other FMDV sequences and can generate cleavage in the presence of heterologous sequences. Insertion of this sequence between two protein coding regions results in the formation of a self-cleaving chimera which cleaves itself into a C-terminal fragment which carries the C-terminal proline of the 2A protease on its N-terminal end, and an N-terminal fragment that carries the rest of the 2A protease peptide on its C-terminus (P. deFelipe et al., Gene Therapy 6: 198-208 (1999)). Thus, instead of using a cleavage signal recognizable by a cell-associated protease, the self-cleaving FMDV 2A protease sequence can be employed to link the NIS to the therapeutic polypeptide, resulting in spontaneous release of the NIS from the therapeutic protein.

Ex Vivo

The above disclosure describes a method of determining transgene localization whereby the transgene is expressed as a fusion protein comprising the transgene product together with a NIS and a protease-cleavable linker peptide, or where the transgene is operable associated with a first promoter, while the sequence encoding the NIS is operably associated with a second promoter, or where the transgene and the sequence encoding the NIS are separated by a sequence encoding an IRES. With that method, the construct is used to transfect the cell, tissue, organ, or organism that is the target of gene therapy. The same nucleic acids can also be utilized in another fashion, whereby cells previously transfected with the nucleic acid (host cells; FIGS. 8 and 9) are transferred to a mammal, followed by administration of labeled iodine to visualize transgene localization. The host cell selected to receive the nucleic acid according to the invention may be found in situ within the mammalian recipient of the therapy, or the host cell can be a cell isolated from the mammal or from another source, and transfection with the nucleic acid can take place in vitro using standard techniques (e.g., the addition of calcium phosphate solutions or lipids known to induce transfection). The construct itself or a cell transfected in vitro with the construct can be introduced into the mammal by any suitable means known in the art, such as by injection, ingestion, or implantation.

In a variation of this embodiment, one or more cells that have been transfected with the nucleic acid construct described above is introduced to a mammal as a “marker cell” along with one or more cells which have been transfected with a nucleic acid construct comprising a nucleotide sequence which encodes the transgene, but not the NIS. The marker cell, accordingly, is used merely for monitoring the localization of the transgene and is present only in sufficient amount to transport iodine and detect the transported iodine. Where the marker cells for monitoring transgene localization are solely for monitoring purposes and not for treatment purposes, a cell(s) of the mammal (or from another source) is transfected in vitro using a vector described herein, containing both the transgene and the NIS gene (in any of the embodiments described herein), or a vector encoding only the NIS (FIGS. 10 and 11). Thus, cells administered for therapeutic purposes, i.e., containing a transgene, may comprise a small number of cells (i.e., 1%, 2%, 5%, 10%) containing both the transgene and the NIS gene, with the remaining large number of cells (90% or more) containing only the transgene. Alternatively a large proportion of cells (i.e., 60%, 75%, 90%, 100%) may contain both the transgene and the NIS gene, with the remaining cells (e.g. 40%, 25%, 10%) containing only the transgene.

The transfected marker cell(s) is introduced into the mammal concurrently with the introduction of cells transfected with a nucleic acid construct that encodes the transgene alone. Preferably, the marker cells carrying the construct of this invention are targeted to the same tissue or organ as cells carrying the therapeutic transgene for optimal localization of the therapeutic transgene. Expression of the NIS and subsequent sequestration of administered labeled iodine is used to determine the location of the transgene as described above The marker cells can alternatively be transfected with a construct that does not encode a protease-cleavable linker, but instead includes a second promoter which is associated with the sequence encoding the NIS. Another alternative is to transfect the marker cells with a construct that is transcribed to a polycistronic mRNA which comprises an internal ribosome entry site between the transgene and the sequence encoding the NIS. Because of the position of the ribosome entry site, both the transgene product and the NIS may be expressed separately without the need for protease cleavage.

Dosage and Mode of Administration

A nucleic acid according to the invention or a host cell containing the nucleic acid according to the invention may be administered in a pharmaceutical formulation, which comprises the nucleic acid or host cell mixed in a physiologically acceptable diluent such as water, phosphate buffered saline, or saline, and will exclude cell culture medium, particularly culture serum such as bovine serum or fetal calf serum, <0.5%. Administration may be intravenous, intraperitoneally, nasally, etc.

The dosage of nucleic acid according to the invention or cells containing the nucleic acid according to the invention will depend upon the disease indication and the route of administration, but should be generally between 1-1000 μg of DNA/kg of body weight/day or 10³-10⁹ transfected cells/day. In embodiments comprising the administration of cells for therapeutic purposes, i.e., cells containing a transgene, the cells may comprise a small number (i.e., 1%, 2%, 5%, 10%) containing both the transgene and the NIS gene, or alternatively a large proportion of cells (i.e., 60%, 75%, 90%, 100%) containing both the transgene and the NIS gene. The dosage of nucleic acid, or cells containing nucleic acid encoding an NIS will be according to the same numerical guidelines provided above for a therapeutic nucleic acid or cell containing a therapeutic nucleic acid

The duration of treatment will extend through the course of the disease symptoms and signs (clinical features), possibly continuously. Monitoring of NIS is performed at any time during the course of treatment. The number of doses will depend upon disease delivery vehicle and efficacy data from clinical trials. Symptoms for a given disease are indicated by the conventional clinical description of the disease, and will be selected for monitoring by the physician treating the disease. For example, the symptoms of cancer are well-known for each type of cancer. One clinical sign for cancer assessment, for example, is tumor size, which can be measured as an indicator of disease response to treatment. When clinical symptoms are assessed, the physician monitors the symptoms and evaluates whether the symptoms are getting worse or better as the disease progresses or recedes, respectively. One such example is monitoring the destruction of certain cell types that are malignant as an indicator of the success of treatment.

Kits

Another embodiment of the present invention is a kit containing a nucleic acid construct according to the invention and one or more reagents for the localization of the NIS, wherein the tissue distribution of the NIS is indicative of the distribution of the polypeptide encoded by the transgene. Reagents for detecting the NIS can include any detectable moiety complexed with iodine, such as radiolabeled iodine, wherein the use and distribution of the radiolabeled iodine complies with Federal radiation safety guidelines. An alternative kit would contain a cell according to the invention that has previously been transfected with the construct according to the invention together with one or more reagents for detection of the NIS. Either kit can include a set of instructions for using the construct or cell and for quantifying the NIS, for example, by SPECT or PET scanning.

Localization of the Transgene

The mammals are maintained on a low iodine diet for two weeks prior to the introduction of the nucleic acid construct by any of the methods described herein. A tracer dose of about 5-10 mCi, preferably about 1-5 mCi, and more preferably about 0.1-1 mCi of ¹³¹I, ¹²⁴I, or ¹²³I is administered by the intraperitoneal, or intravenous route at 24 hours, 48 hours, 96 hours, and 8 days following administration of the vector according to the invention. The syringe used to deliver the radioiodine is counted prior to and following iodine injection to verify the dose of radiation administered to the mammal. One hour after radioiodine injection, anterior and posterior images are taken using SPECT, or PET scans. Images according to the invention, may be taken of the whole body, or of specific regions, or organs. Image acquisition may be repeated at 2, 6 and 24 hours post-injection. Regions of uptake are mapped, and quantified (if using the PET method) and expressed as a fraction of the total amount of the administered radioiodine. Thus, detection of transported iodine as indicative of the presence of a transgene is that detection which the radiologist or physician determines qualitatively to be an image indicating transport of labeled iodine. The qualitative indication may be an area of the host body which is darker or denser in the scan, indicating sequestration of labeled iodine. Quantitative detection of transported labeled iodine indicative of the presence of a transgene is that percentage of the total labeled iodine administered that is above 1% and preferably about 10%.

Imaging with ¹²⁴I PET will offer higher resolution imaging, higher sensitivity, attenuation correction, more accurate tumor localization and more accurate quantitation of uptake than is currently possible with conventional gamma cameras (Pentlow et al., Medical Physics 18: 357-366 (1991); Pentlow et al., J. Nuc. Med. 37: 1557-1562 (1996)) The physical characteristics of ¹²⁴I including a half life of 4.2 days make it highly suitable for direct imaging of tissues capable of concentrating iodide, such as thyroid. Moreover, ¹²⁴I is well suited for imaging of tissues which sequester iodine due to the expression of an exogenous NIS. Previous studies have demonstrated high resolution images and the ability to carefully quantitate iodide uptake and efflux by thyroid glands using this radionuclide (Crawford et al., Eur. J. Nuc. Med. 24: 1470-1478 (1997)) and positron emission tomography. Further, ¹²⁴I PET has been shown to yield more accurate dosimetry measurements than conventional ¹³¹I (Ott et al., Br. J. Radiol. 60: 245-251 (1987); Flower et al., Br. J. Radiol. 63: 325-330 (1990); Flower et al., Eur. J. Nuc. Med. 21:531-536 (1994)). Potential for use of ¹²⁴I to radioiodinate proteins such as antibodies or enzyme substrates and image their distribution to target tissues is also high, but has to date been investigated only in a small number of studies (Rubin et al. Gyn Oncol. 48:61-7, (1993); Arbit et al., Eur J Nuc Med 22:419-26, (1995); Tjuvajev et al. Cancer Res. 58:4333-41, (1998); Gambhir et al., J Nuc Med. 26:481-90, (1999)).

According to the present invention, ¹²⁴I PET imaging will allow improved assessment of NIS activity and transgene distribution in mammals following administration of the nucleic acid construct bearing the transgene and a sequence encoding the NIS. In addition, ¹²⁴I PET imaging permits more accurate dosimetry, which will allow optimization of the therapeutic responses. The techniques of both SPECT and PET are well described in the art, and are exemplified in the following references: Pentlow et al., Medical Physics. 18:357-66 (1991); Pentlow et al., J Nuc Med. 37:1557-62 (1996); Biegon, U.S. Pat. No. 5,304,367. The studies will also provide models of this technology for use in other tumor types and in other gene transfer experiments in which NIS is used as a therapeutic gene.

EXAMPLES Example 1 Construction of Fusogenic Membrane Glycoproteins (FMG) Linked to NIS Expression Plasmids

Expression plasmids were prepared with the nucleotide sequence encoding NIS linked to two different FMGs: gibbon ape leukemia virus (GALV; Delassus et al., Virology 173: 205-213, 1989) hyperfusogenic envelope lacking the cytoplasmic R-peptide and measles virus H glycoprotein (deStuart et al., Lancet 355: 201-202, 2000). Expression constructs were made using furin-cleavable or non-cleavable linkers to connect the 644 amino acid NIS to either the N-terminus of GALV (FIG. 6) or the C-terminus of Measles H glycoprotein (FIG. 7).

Example 2 In Vivo Gene Transfection Using Adenovirus

We have developed a replication-deficient human recombinant type 5 adenovirus (Ad5) carrying the human NIS gene linked to the CMV promoter (Ad5-CMV-NIS). LNCaP (human prostate cancer cell line) xenografts were established in nude mice and grown to approximately 5 mm diameter. Thereafter, 150 μL (3×10¹⁰ PFU in 3% sucrose/phosphate buffered saline) of Ad5-CMV-NIS (right flank) or control virus (left flank) was injected directly into the tumors using tuberculin syringes. The needle was moved to various sites within the tumor during injection to maximize the area of virus exposure. Four days following intratumoral injection of Ad5-CMV-NIS (right flank) or control virus (left flank), mice were injected intraperitoneally with of 500 μCi ¹²³I and radioiodine imaging was performed using a gamma camera. Regions of uptake were quantified and expressed as a fraction of the total amount of the applied radioiodine. Iodide retention time within the tumor was determined by serial scanning following radioiodine injection, and dosimetric calculations were performed. Tumors were removed and evaluated for NIS expression by western blotting and by immunohistochemistry. In a second group of mice a single injection of 3 μCi ¹³¹I was given IP and the mice observed over time for therapeutic responses as described in section 10 above. Ad5-CMV-NIS transfected tumors readily trapped iodide and could be imaged with a gamma camera. The average uptake in 5 mice was 22.5±10.0% of the injected radioiodine dose. In contrast, tumors transfected with control virus constructs demonstrated no uptake of radioiodine and no image on the gamma camera. NIS protein expression was confirmed by western blotting and by immunohistochemistry.

Other Embodiments

Other embodiments will be evident to those of skill in the art. It should be understood that the foregoing detailed description is provided for clarity only and is merely exemplary. The spirit and scope of the present invention are not limited to the above examples, but are encompassed by the following claims.

TABLE 1 Properties of some proteases associated with post-translational processing. Subcellular Tissue Nucleotide Protease Localization Distribution Cleavage Signal Sequence furin Golgi ubiquitous RXKR tctnnnttttct (SEQ ID NO: 7) (SEQ ID NO: 8) MMP-2 Golgi tumor cells PLGLWA cctaatcctaatacccgt (SEQ ID NO: 9) (SEQ ID NO: 10) MT1-MMP plasma membrane tumor cells PLGLWA cctaatcctaatacccgt (SEQ ID NO: 11) (SEQ ID NO: 12) caspase- 1 secretory pathway ubiquitous YEVDGW atccttcatctgcctacc (SEQ ID NO: 13) (SEQ ID NO: 14) caspase-2 VDVADGW catctgcatcgtctgcct (SEQ ID NO: 15) acc (SEQ ID NO: 16) caspase-3 VDQMDGW catctggtttacctgcct (SEQ ID NO: 17) acc (SEQ ID NO: 18) caspase-4 LEVDGW aatcttcatctgcctacc (SEQ ID NO: 19) (SEQ ID NO: 20) caspase-6 VQVDGW catgttcatctgcctacc (SEQ ID NO: 21) (SEQ ID NO: 22) caspase-7 VDQVDGW catctggttcatctgcct (SEQ ID NO: 23) acc (SEQ ID NO: 24) alpha- secretory pathway ubiquitous amyloid  amyloid precursor secretase precursor protein (APP) protein (APP) proprotein endoplasmic ubiquitous brain  tctcctaattgt convertase reticulum neurotrophic (SEQ ID NO: 26) (subtilisin/ growth factor kexin isozyme precursor  SKI-1) (RGLT (SEQ ID NO: 25)) proprotein secretory pathway ubiquitous convertases  (PC-2, PC-3, etc.) tumor  tumor cells associated trypsin foot and mouth NFDLLKLAGDVES ttgaagctgaataatttta disease virus, NPGP atcgtcctctgcatctttc protease 2A (SEQ ID NO: 5) gttgggtcctggt (SEQ ID NO: 6) 

1. A nucleic acid construct comprising a first promoter, a second promoter, a sequence encoding a fusogenic polypeptide, and a sequence encoding a sodium-iodide symporter, wherein said first promoter regulates expression of the sequence encoding said polypeptide, and wherein said second promoter regulates expression of the sequence encoding said sodium-iodide symporter.
 2. The nucleic acid construct of claim 1, wherein said fusogenic polypeptide is a viral fusion protein.
 3. The nucleic acid construct of claim 1, wherein said fusogenic polypeptide is a measles virus H glycoprotein.
 4. The nucleic acid construct of claim 1, wherein said fusogenic polypeptide is a gibbon ape leukemia virus envelope glycoprotein.
 5. A kit comprising: (a) a nucleic acid construct or a cell transfected with said nucleic acid construct, wherein said nucleic acid construct comprising a first promoter, a second promoter, a sequence encoding a fusogenic polypeptide, and a sequence encoding a sodium-iodide symporter, wherein said first promoter regulates expression of the sequence encoding said fusogenic polypeptide, and wherein said second promoter regulates expression of the sequence encoding said sodium-iodide symporter, and (b) a reagent for monitoring the location of said fusogenic polypeptide.
 6. The kit of claim 5, wherein said reagent comprises labeled iodine or radioactive iodine. 